Sometimes, it's just too hot to fly

And it's not because the planes will melt.

We're all familiar with the rampant cancellation of flights due to winter-related weather. Blizzards wreak havoc with the U.S.'s air traffic system and create a long chain of cancelled flights, delayed trips and stranded passengers that turn airports into uncomfortable hotels.

But summer is different! There's plenty of sunshine and nary a snowflake in sight that threatens to derail any air travel plans. Sadly, we may need to adjust our expectations if what happened in Phoenix today is a sign of things to come.

American Airlines cancelled almost 50 flights from Sky Harbor International Airport in Arizona's capital city since the June 20 forecast called for temperatures to reach 120 degree Fahrenheit. These flights, all regional ones according to the Arizona Republic, were scheduled to take off between 3 p.m. and 6 p.m. local time, aka the hottest time of day.

The planes, all Bombardier CRJ aircraft, have maximum operating temperature of 118 degrees. But what does that mean, exactly? Do the planes melt if it gets any hotter than 118 degrees? Or are humans just not meant to be in planes at such high temperatures, or else we'll suffer from "Twilight Zone"-esque visions of monsters on the wings?

It's nothing so dramatic. It's just science, but a science we may want to get used to.

A lot of hot air

The engines and wings work together to get planes up in the air. (Photo: biggaju/Shutterstock)

You may think it's the engines that lift a plane up, up and away, but the engines are there to move a plane forward, not up. The "up" is provided by the wings. As planes gain speed, the air moves rapidly only over the tops of the wings and decreases the overall air pressure. However, there's still plenty of pressure below the wings, and the difference in pressure between the top and bottom of the wings creates lift. Lift gets you up into the air.

So what what does this have to do with 120-degree weather?

When air is hotter, it's less dense. And the less dense the air is, the further the plane has to move forward to create the necessary differences in air pressure to create lift. However, there may not be enough runaway to do that, and so the plane can't take off. And even if you had enough runaway, things like the weight of the passengers and their baggage and the surrounding landscape would all play a role in whether or not the plane could take off with the reduced lift.

Larger planes, like Airbuses, have a higher operating temperature, so they're not affected by the heat as much, but that's not to say they will always been immune to this problem in the future, as temperatures continue to rise.

Flying the heated skies

Dealing with hot air and reduced lift is already a fact of life in some areas.

But these are both areas where schedules and airports were designed with local temperatures and air densities in mind. The U.S. hasn't really had to worry about such extreme temperatures before, and instances like today or similar one that occurred in 2013, would seem to indicate that airports and airlines start seriously thinking about warming temperatures.

That same ICAO report more or less said the same thing, albeit with a more ominous tone: "Aviation is an extremely risk averse business. Climate change poses a new set of risks that airports need to assess properly. The last decades have provided a glimpse of the future climate, but the main effects will be more evident three or four decades from now, and onwards."